disintegration solubility diss (lecture 3)

Question 1

Definition

Answer 1

Definition: It is the process by which a solid (the solute) dissolves into a liquid solvent becoming molecularly mixed in the liquid state homogenously - A thermodynamic process driven by ΔG - Must be thermodynamically favorable and spontaneous - Equilibrium conditions - Entropy of the system increases - Thermodynamically stable - Reverse thermodynamic process is precipitation

Question 2

The dissolution rate

Answer 2

The dissolution rate: mass of solid dissolved/time - is a rate - is a kinetic process - Measured under controlled standard conditions

Question 3

Solubility

Answer 3

Solubility: maximum amount (saturated) of drug solute dissolved in a solvent - units of concentration

Question 4

Solubility & Dissolution

Answer 4

• Solubility can be low, but the dissolution rate can be fast •Solubility can be high, but the dissolution rate can be slow

Question 5

USP Solubility Definitions & Units

Answer 5

Question 6

Dissolution Testing

Answer 6

For oral dosage form pharmaceutical development, solubility is determined by dissolving drug in 250mL buffer (8 oz)

Dissolution medium: depend on the target organ
• pH range: pH 1.2 – 6.8 (oral dosage forms) vs. pH 7.0-7.4 • Temperature: 37oC + 0.5oC

Question 7

Factors Affecting Drug Absorptio

Answer 7

Rate-Limiting Steps in Drug Absorption

• Slowest step = the rate-limiting step
• Generally, tablet disintegration is the fastest step.

Dissolution is often rate-limiting for poorly water-soluble drugs having low aqueous solubility.

Permeability is often rate-limiting for highly water-soluble drugs having high aqueous solubility.